#define _CRT_SECURE_NO_WARNINGS 1
#include<bits/stdc++.h>
using namespace std;

int main()
{
	int n;
	cin >> n;
	int empty = 0;
	while (n)
	{
		n--;
		empty++;
		if (empty % 3 == 0)
			empty++;
	}
	cout << empty << endl;
}